Permanent magnet dynamo electric machine

ABSTRACT

In order to realize a permanent magnet dynamo electric machine which permits a high speed rotation, the permanent magnet dynamo electric machine including a stator  20  having a stator iron core  22  in which a stator winding  24  is wound, and a rotor  30  facing the inner circumference of the stator  20  and rotatably supported thereby, the rotor  30  having a rotor iron core  32  and a plurality of permanent magnets  36  arranged inside the rotor iron core  32  so as to face the stator iron core  22 , wherein the rotor iron core  32  is provided with the same number of permanent magnet insertion holes  34  as the plurality of permanent magnets  36  for receiving the same at positions where ratio R 1 /R 0  is equal to or more than 0.85, wherein R 0  is the radius of the rotor  30  and R 1  is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets  36  at the side remote from the stator  20.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a permanent magnet dynamo electric machine and, in particular, relates to a permanent magnet dynamo electric machine having embeded permanent magnets inside the rotor thereof.

[0003] 2. Description of Related Art

[0004] There are two types of conventional permanent magnet dynamo electric machines, in that, in one type the permanent magnets are secured on the circumference of the rotor thereof, and in the other type the permanent magnets are embeded inside the rotor thereof. JP-A-5-76146 (1993) discloses a structure of the latter type.

[0005] In the permanent magnet dynamo electric machine having a structure of the latter type, when the rotor thereof is rotating, centrifugal forces acting on the respective permanent magnets are applied to rotor members located along the outer circumferences of the respective permanent magnets. Further, the rotor members themselves are subjected to centrifugal forces. Members which locate at both circumferential ends of the rotor members, namely bridge portions, support the above mentioned two sorts of the centrifugal forces. Therefore, in order to withstand centrifugal forces caused by high speed rotation, the thickness of the bridge portions has to be increased.

[0006] On the other hand, when the thickness of the bridge portions is thickened, magnetic fluxes generated by the permanent magnets leak via the bridge portions to the surrounding iron core, and amount of magnetic fluxes transferred from the surface of the rotor to the stator thereof is decreased. Torque generated by the permanent magnet dynamo electric machine depends on the amount of magnetic fluxes transferred from the permanent magnets to the stator, therefore, if magnetic flux leakage increases, the torque generated decreases and the effeciency of the permanent magnet dymano electric machine reduces accordingly.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a permanent magnet dynamo electric machine having embeded permanent magnets inside the rotor thereof which permits high speed rotation as well as enhances efficiency thereof by means of suppressing magnetic flux leakage via bridge portions while limiting loads due to centrifugal forces applied to the bridge portions.

[0008] The object of the present invention is resolved by a permanent magnet dynamo electric machine comprising a stator having a stator iron core in which a stator winding is wound, and a rotor facing the inner circumference of the stator and rotatably supported thereby, the rotor being constituted by a columnar rotor iron core, a shaft provided along the rotation axis of the rotor iron core and a plurality of permanent magnets arranged in a ring shape along the circumference of the rotor iron core so as to face the stator iron core, characterized in that, the rotor iron core is provided with the same number of permanent magnet insertion holes as the plurality of permanent magnets for receiving the same at positions where ratio R1/R0 is equal to or more than 0.85, wherein R0 is the radius of the rotor and R1 is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets at the side remote from the stator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 shows a partial cross sectional view of a permanent magnet dynamo electric machine seen from the front thereof representing one embodiment according to the present invention;

[0010]FIG. 2 shows a cross sectional view taken along the line II-II in FIG. 1;

[0011]FIG. 3 shows an enlarged view of a major portion shown in FIG. 2;

[0012]FIG. 4 shows a cross sectional view of a rotor of a permanent magnet dynamo electric machine representing another embodiment according to the present invention;

[0013]FIG. 5 shows a cross sectional view of a rotor of a permanent magnet dynamo electric machine representing still another embodiment according to the present invention;

[0014]FIG. 6 shows a magnetic flux density distribution along an air gap in the permanent magnetic dynamo electric machine shown in FIG. 5;

[0015]FIG. 7 shows a cross sectional view of a rotor of a permanent magnet dynamo electric machine representing yet another embodiment according to the present invention;

[0016]FIG. 8 shows a cross sectional view of a rotor of a permanent magnet dynamo electric machine representing a further embodiment according to the present invention;

[0017]FIG. 9 shows a cross sectional view of a rotor of a permanent magnet dynamo electric machine representing a still further embodiment according to the present invention; and

[0018]FIG. 10 shows a block diagram of an electric car mounting a permanent magnet dynamo electric machine according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In FIG. 1, a stator 20 in a permanent magnet dynamo electric machine 10 is constituted by a stator iron core 22, a poly phase stator winging 24 wound in the stator iron core 22 and a housing 26 which fixedly secures the stator iron core 22 at the inner circumferential face thereof.

[0020] A rotor 30 is constituted by a rotor iron core 32, a shaft 38 therefor and a plurality of permanent magnets 36.

[0021] The rotor iron core 32 is formed by laminating in axial direction a plurality of sheets of magnetic material having a high reameability such as silicon steel sheet. As will be seen from FIGS. 1 and 2, the respective lamination sheets are provided with punched through permanent magnet insertion holes 34 and a punched through hole for receiving the shaft 38 in the axial direction, and the respective permanent magnets 36 and the shaft 38 are inserted in the corresponding punched through holes.

[0022] The shaft 38 is rotatably held by bearings 42 and 44 with respect to the stator 20. The bearings 42 and 44 are respectively supported by end brackets 46 and 48, and these end brackets 46 and 48 are fixedly secured to the respective ends of the housing 26.

[0023] At one side of the rotor 30, a magnetic pole position detector PS for detecting positions of the permanent magnets 36 in the rotor 30 and an encoder E for detecting position of the rotor 20 are arranged. The permanent magnet dynamo electric machine 10 is operated and controlled through a control unit (not shown) depending on signals from the magnetic pole position detector PS and the encoder E.

[0024]FIG. 2 is a cross sectional view taken along the line II-II and seen in the arrowed direction in which illustration of the housing 26 is omitted.

[0025] The rotor iron core 32 is provided with eight permanent magnet insertion holes 34 having a rectangular shape in cross section which are arranged in a ring shape as a whole so as to face the stator iron core 22 and eight permanent magnets 36 having substantially the same configuration are inserted in the respective permanent magnet insertion holes 34. Since the cross section of the respective permanent magnets 36 is rectangular as seen from the drawings, the respective permanent magnets 36 are accurately dimensioned in comparison with permanent magnets having an arcuate cross section, thereby a permanent magnet dynamo electric machine, which permits a high speed rotation without any balancing work on the rotor, is provided.

[0026] The eight permanent magnets 36 are positioned with a same spacing along the circumference of the rotor iron core 32 in such a manner that the polality of adjacent one is opposite each other. Further, along the center portion of the rotor iron core 32 the shaft 38 is inserted. In the present embodiment it is assumed that the permanent magnet type rotor 30 is designed to rotate in anti-clockwise direction.

[0027]FIG. 3 is an enlarged view of a part of FIG. 2.

[0028] When classifying the area of the rotor iron core 32 into two in its radial direction, one is a yoke portion 32A at the inner circumferential side and the other is an outer circumferential portion 32B. Further, the outer circumferential portion 32B is further classified into three in that, a magnetic pole piece portion 32B1, auxiliary magnetic pole piece portion 32B2 and a bridge portion 32B3.

[0029] The magnetic pole piece portion 32B1 is located at the immediate outer circumference of the permanent magnet 36 and is an area constituting a magnetic circuit which passes magnetic flux Bφ generated by the permanent magnet 36 to the side of the stator 20 via an air gap between the rotor 30 and the stator 20.

[0030] The auxiliary pole piece portion 32B2 is an area between two adjacent magnetic pole piece portions 32B1 which permits to pass magnetic fluxes generated by magneto motive forces of the stator winding 24 while bypassing the magnetic circuits for the permanent magnets 36. When a composite vector of armature magneto motive forces caused by currents flowing through the stator winding 24 is controlled by the control unit not shown so as to direct in rotating direction with reference to the center position of the auxiary magnetic pole piece portion 32B2, the permanent magnet dynamo electric machine 10 can generate a torque due to the auxiliary pole piece portion 32B2 in addition to the torque due to the permanent magnets 36 and thereby can operate as a high torque electric motor.

[0031] The bridge portion 32B3 is a boundary portion between the magnetic pole piece portion 32B1 and the auxiliary magnetic pole piece portion 32B2 and also a portion where the outer circumference of the permanent magnets 36 is nearest to the outer circumference of the rotor iron core 32.

[0032] When the rotor 30 is rotated, respective elements constituting the rotor 30 are subjected to centrifugal forces. Among these centrifugal forces, the centrifugal forces acting on the permanent magnets 36 and the magnetic pole piece portions 32B1 located at the outer circumferential side of the permanent magnets 36 are concentrated on the bridge portions 32B3. Therefore, the bridge portions 32B3 are likely to be broken.

[0033] For countermeasuring such problem, it is conceived to increase the thickness of the bridge portions 32B3, however, with such countermeasure leakage flux B_(L) via the bridge portion 32B3 increases to thereby decrease torque generated by the permanent magnet dynamo electric machine. If a predetermined torque is required to be generated even with the increased leakage flux B_(L), the size of the permanent magnet dynamo electric machine itself has to be increased which prevents a high speed rotation thereof.

[0034] Therefore, the permanent magnet insertion holes 34 are formed in the rotor 30 at positions ratio R1/R0 is equal to or more than 0.85, wherein R0 is the radius of the rotor 30 and R1 is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets 36 at the side remote from the stator 20.

[0035] In the embodiment shown in FIG. 3, in order to fulfill the above condition R0 and R1 are respectively set at 57.5 mm and at 49.5 mm. Further, the thickness R3 of the permanent magnets 36 in the radial direction, the maximum thickness R4 of the magnetic pole piece portion 32B1 in the radial direction and the thickness R2 of the bridge portion 32B3 in the radial direction are respectively set at 4 mm, 4 mm and 2 mm.

[0036] When the ratio R1/R0 is determined equal to or more than 0.85, the centrifugal force caused by the permanent magnets 36 is reduced less than ½ of the centrifugal force caused by the entire rotor 30 and the load which has to be beared by the bridge portion 32B3 is decreased. Further, it is unnecessitated to needlessly increase the thickness R2 of the bridge portions 32B3 in comparison with when the ratio R1/R0 is set less than 0.85, and the leakage flux B_(L) is reduced. Accordingly, generating torque reduction is prevented and a high speed rotation is realized.

[0037] Further, in order to achieve a high speed rotation, it is preferable to reduce the thickness of the permanent magnets 36 as much as possible. In particular, in the present embodiment, the thickness R3 of the permanent magnets 36 is determined equal to or less than two times of the thickness of the bridge portions 32B3. Thereby, a permanent magnet dynamo electric machine which can rotate at a high speed is realized.

[0038] R1/R0 ratio of the structure shown in FIG. 1 of JP-A-5-76146 (1993) as indicated in the introductory portion of the present specification is 0.72 (2.1/2.9). With this structure the centrifugal forces concentrated at the bridge portions amount 1.5 times as that of the present embodiment as shown in FIG. 3, therefore, the thickness of the bridge portions has to be increased which as a matter of course increases leakage fluxes passing therethrough.

[0039] With the structure of the present embodiment, the leakage fluxes are reduced, thereby the reduction of torque generation in the permanent magnet dynamo electric machine is prevented. As a result, the size and weight of the permanent magnet dynamo electric machine are reduced, thereby the permanent magnet dynamo electric machine is permitted to rotate at a high speed.

[0040] In FIG. 4, the rotor 30 according to FIG. 2 embodiment is provided additionally with a plurality of vents 39. Since the permanent magnets 36 are arranged at the outer circumferential side of the rotor 30, the magnetic flux density in the yoke portion 32A at the inner circumferential side of the rotor iron core 32 is extremely low. Therefore, if the same number of vents 39 as that of the permanent magnets 36 are formed in the yoke portion 32A, the amount of fluxes generated by the rotor 30 is substantially inaffected.

[0041] The radial distance R5 of the face at the inner circumferential side and the radial distance R6 of the face of the outer circumferential side of the vent 39 are respectively set at 27 mm and 17 mm, and the circumferential width of the face at the outer circumference of the vent 39 is equated with the width of the permanent magnet 36. Thereby, the total weight of the rotor 30 of the present embodiment is reduced by 27% in comparison with FIG. 2 embodiment with no provision of the vents 39.

[0042] As a result, the weight of the rotor 30 is lightened, and the entire weight of the permanent magnet dynamo electric machine is accordingly reduced which permits a high speed rotation thereof. Further, the loads on the bearings 42 and 44 are also lightened.

[0043] It is effective to set the total opening area of all the vents 39 more than 20% of the cross sectional area of the rotor 30. Further, it is preferable that the number of the vents 39 is to be equal to that of the permanent magnets 36. However, the number of the vents 39 can be less than that of the permanent magnets 36. In such instance, it is preferable to set the number of the vents 39 at one/permanent magnets 36 in view of the rotation balance thereof.

[0044] Further, the provision of the vents 39 is particularly effective when permanent magnets 36 of rare earth elements are used of which magnetic flux reduces significantly due to temperature rise thereof. Namely, through the provision of the vents 39 of the same number as the permanent magnets 36, cooling wind is introduced into the inner circumference of the rotor 30 and the temperature of the permanent magnets 36 is kept low, thereby the amount of magnetic fluxes caused thereby is increased and the rotation torque thereby can correspondingly be increased.

[0045]FIG. 5 is a modification of FIG. 4 embodiment in which the circumferential length of the permanent magnet insertion holes 34 is selected longer than that of the permanent magnets 36 to thereby form gaps 52 and 54 at the respective bridge portions 32B3. The gaps 52 and 54 at the bridge portions 32B3 provided at the rotor iron core 32 can be filled with such as an adhesive. Further, clearances at radially outer circumference of the permanent magnets 36 can likely be filled with such as an adhesive, thereby, a tough rotor structure is realized.

[0046]FIG. 6 is a view for explaining a magnetic flux density distribution in FIG. 5 embodiment. As illustrated by a solid line in FIG. 6, the magnetic flux density generated by the permanent magnet 36 along the air gap facing the permanent magnet 36 is uniform, and the magnetic flux densities at both end portions of the permanent magnet 36 are gentlely inclined in the circumferential direction because of the existence of the gaps 52 and 54. Dotted lines in FIG. 6 show an assumed magnetic flux density distribution when the length of the permanent magnet insertion hole 34 is equated with that of the permanent magnet 36 wherein the magnetic flux density is steeply varied at the both end portions of the permanent magnet 36.

[0047] Through the provision of the gaps 52 and 54 for the bridge portions 32B3 between the magnetic pole pieces 32B1 and the auxiliary magnetic pole pieces 32B2 and at the inner circumferential side thereof, the variation of magnetic flux density along the air gap in the circumferential direction is gentled, thereby generation of rippling torque and cogging torque can be reduced.

[0048] Further, with the structure according to the present embodiment, amount of permanent magnets to be used is also reduced. Since the permanent magnets of rare earth elements are expensive, the amount reduction of the permanent magnets is effective for reducing the cost of the permanent magnet dynamo electric machine. Even when the amount of permanent magnets is reduced according to the present embodiment, because of the existence of the gaps 52 and 54 at both circumferential ends of the permanent magnets 36 possible leakage fluxes toward the auxiliary magnetic pole pieces 32B3 are reduced, thereby a possibility of torque reduction is prevented.

[0049]FIG. 7 is a modification of FIG. 5 embodiment in which a single gap 52 is provided at one circumferential end of the permanent magnet and further the permanent magnets 36 are configurated in an arcuate shape.

[0050] In the present embodiment, since it is assumed that the rotor 30 is designed to be rotated in only one direction as indicated by the arrow B, the permanent magnets 36 are inserted into the permanent magnet insertion holes 34 while shifting the permanent magnets 36 toward one side in the rotation direction B.

[0051] When an electrically driven motor vehicle runs backward, the wheels are rotated in the reverse direction by means of a change gear mechanism. Therefore, it is sufficient if the permanent magnet dynamo electric machine is designed to be rotatable only in one direction and thus if the rotating torque generated by the permanent magnet dynamo electric machine in the predetermined rotation direction is also sufficient, a small rotating torque in the opposite direction (clockwise direction) to the arrowed direction B can be acceptable.

[0052] Accordingly, as illustrated in FIG. 7, the permanent magnets 36 are inserted in the permanent magnet insertion holes 34 in such a manner to shift toward to rotating direction B and the gap portions 52 are formed at positions adjacent to the anti-rotating direction of the permanent magnets 36, thereby a possibly magnetic flux leakage along the gap portions 52 is suppressed. Likely, centrifugal forces caused by the permanent magnets 36 are reduced which realizes a structure suitable for a high speed rotation.

[0053] The gap portions 52 formed at the anti-rotating direction of the permanent magnets 36 are, for example, filled with such as varnish, thereby the rotor structure is strengthened.

[0054]FIG. 8 is a modification of FIG. 7 embodiment in which gap portions 56 are formed at the opposite direction to the rotating direction B of the permanent magnet insertion holes 34 along the outer circumferential side thereof. The permanent magnet dynamo electric machine is designed to be rotatable only in the arrowed direction B like FIG. 7 embodiment.

[0055] The permanent magnet insertion holes 34 are configurated to have a larger opening than the permanent magnet 36 to be inserted at the opposite side to the rotating direction B of the rotor 20. As a result, rotating torques generated by the permanent magnet dynamo electric machine is sufficient large for the rotating direction B but small for the opposite direction (clockwise direction) of the arrowed direction B. However, through the formation of the gap portions 56 at the anti-rotating direction of the permanent magnets 36, magnetic flux leakage along the gap portions 56 is limitated and the magnetic fluxes generated by the permanent magnets 36 are effectively utilized.

[0056] Further, in the present embodiment radial direction thickness of the magnetic pole pieces 32B1 which is located along the outer circumference of the permanent magnet 36 is different at positions along the circumference thereof. More specifically, the thickness t1 of the magnetic pole piece 32B1 at the side of anti-clockwise direction is thicker than the thickness t2 of the magnetic pole piece 32B1 at the side of clockwise direction. With thus constituting the permanent magnet insertion holes 34, during no load operation of the permanent magnet dynamo electric machine magnetic fluxes leak via the magnetic pole pieces 32B1 at the side of anti-clockwise direction B to the yoke portion of the rotor iron core 32 and its induced voltage is limited low. Accordingly, at the time of an inverter failure during a high speed rotation of the permanent magnet dynamo electric machine a possible large current flow into a battery is prevented and thereby provisions such as contactors can be omitted.

[0057]FIG. 9 is another modification of FIG. 4 embodiment in which a pair of slits 62 and 64 are formed at both ends of the permanent magnet insertion holes 34.

[0058] These slits 62 and 64 correspond to the gaps 52 and 54 as shown in FIG. 5, but are narrowed along their radial direction so as to facilitate the positioning of the permanent magnets 36 in their circumferential direction.

[0059] When the permanent magnets 36 are inserted into the permanent magnet insertion holes 34′, the permanent magnets 36 are attracted to the side of near-by magnetic material by their attraction forces and are rested on magnetically stable inner diameter side thereof, which facilitates injection of adhesives such as varnish onto the outer circumferential side of the permanent magnets 36. Such varnish limits a possible mechanical contact between the permanent magnets 36 and the magnetic pole pieces 32B1 and contributes to provide a permanent magnet dynamo electric machine suitable for a high speed rotation.

[0060]FIG. 10 is a block diagram of an electric car mounting a permanent magnet dynamo electric machine according to the present invention.

[0061] A body 100 of the electric car is supported by four wheels 110, 112, 114 and 116. Since the present electric car is a front wheel drive, a permanent magnet dynamo electric machine 120 is coupled to a front axle 154 via a change gear mechanism not shown. The driving torque of the permanent magnet dynamo electric machine 120 is controlled by a control unit 130. A battery 140 is provided as a power source for the control unit 130 and the electric power of the battery 140 is fed to the permanent magnet dynamo electric machine 120 via the control unit 130 to drive the permanent magnet dynamo electric machine 120 and to thereby rotate the wheels 100 and 114. Rotation of a steering wheel 150 is transmitted to the two wheels 110 and 114 via a steering gear 152 and a transmitting mechanism including such as a tie rod and a knucle arm and a steering angle of the wheels 100 and 114 are varied.

[0062] When the permanent magnet dynamo electric machine according to the present invention is applied to an electrically driven motor vehicle, in particular, to an electric car, a permanent magnet dynamo electric machine driving device of small size and light weight having a high efficiency can be mounted and an electric car having a long running distance per one charging operation is realized.

[0063] Further, the permanent magnet dynamo electric machine can also be applied for driving axles for an electric locomotive. 

1. A permanent magnet dynamo electric machine comprising a stator having a stator iron core in which a stator winding is wound, and a rotor facing the inner circumference of said stator and rotatably supported thereby, said rotor being constituted by a columnar rotor iron core, a shaft provided along the rotation axis of said rotor iron core and a plurality of permanent magnets arranged in a ring shape along the circumference of said rotor iron core so as to face said stator iron core, characterized in that, said rotor iron core is provided with the same number of permanent magnet insertion holes as the plurality of permanent magnets for receiving the same at positions where ratio R1/R0 is equal to or more than 0.85, wherein R0 is the radius of said rotor and R1 is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets at the side remote from said stator.
 2. A parmanent magnet dynamo electric machine according to claim 1 , characterized in that, the thickness of said permanent magnets is selected less than two times of the thickness R2 of a bridge portion in said rotor iron core representing a boundary portion a magnetic pole piece portion locating along the outer circumference of said permanent magnets and auxiliary magnetic pole piece portion locating circumferentially adjacent to said magnetic pole piece portion.
 3. A permanent magnet dynamo electric machine comprising a stator having a stator iron core in which a stator winding is wound, and a rotor facing the inner circumference of said stator and rotatably supported thereby, said rotor being constituted by a columnar rotor iron core, a shaft provided along the rotation axis of said rotor iron core and a plurality of permanent magnets arranged in a ring shape along the circumference of said rotor iron core so as to face said stator iron core, characterized in that, said rotor iron core is provided with the same number of permanent magnet insertion holes as the plurality of permanent magnets for receiving the same at positions where ratio R1/R0 is equal to or more than 0.85, wherein R0 is the radius of said rotor and R1 is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets at the side remote from said stator, and said rotor iron core is further provided with a plurality of vents at the side of said shaft with respect to said permanent magnet insertion holes.
 4. A permanent magnet dynamo electric machine comprising a stator having a stator iron core in which a stator winding is wound, and a rotor facing the inner circumference of said stator and rotatably supported thereby, said rotor being constituted by a columnar rotor iron core, a shaft provided along the rotation axis of said rotor iron core and a plurality of permanent magnets arranged in a ring shape along the circumference of said rotor iron core so as to face said stator iron core, characterized in that, said rotor iron core is provided with the same number of permanent magnet insertion holes as the plurality of permanent magnets for receiving the same at positions where ratio R1/R0 is equal to or more than 0.85, wherein R0 is the radius of said rotor and R1 is the radius of an imaginary circle drawn by inscribing the faces of the plurality of permanent magnets at the side remote from said stator, and the circumferential length of said permanent magnet insertion holes is set longer than that of said permanent magnets so that when said permanent magnets are inserted into the corresponding permanent magnet insertion holes a pair of gaps are formed at both ends of each of said permanent magnets.
 5. A permanent magnet dynamo electric machine according to claim 4 , characterized in that, said gaps are filled with a resin material.
 6. A permanent magnet dynamo electric machine according to claim 1 , characterized in that, each of said permanent magnet insertion holes is provided with a pair of slits at both circumferential ends thereof.
 7. A permanent magnet dynamo electric machine according to claim 1 , characterized in that, a single gap is provided for each of said permanent magnets circumferentially adjacent thereto at the side of anti-rotating direction of said rotor.
 8. A permanent magnet dynamo electric machine according to claim 1 , characterized in that, a single gap is provided for each of said permanent magnets radially adjacent thereto at the side of anti-rotating direction of said rotor. 